The present invention relates generally to apparatus for restraining lateral movement of a reactor core relative to a reactor vessel, and more particularly to a novel lateral restraint assembly which finds particular application in restraining lateral movement of a reactor core relative to a reactor vessel when the core is subjected to high energy lateral loading such as might be encountered during seismic disturbances and the like.
Nuclear reactors, particularly of the high temperature gas-cooled type, conventionally include reactor cores which are housed within shielded core cavities formed in reactor vessels. The reactor cores are conventionally assembled from a plurality of graphite fuel and control elements which may have polygonal shaped outer configuratons and are arranged in stacked column relation so that coolant and control rod passages formed longitudinally of the fuel and control elements are in axially aligned relation. The blocks within each column may be secured together to provide relatively loose lateral support therebetween. Because of thermal expansion, irradiation shrinkage, pressure effects and creep of the reactor vessel, which is conventionally made of prestressed concrete, it has not been practical to clamp the columns of graphite blocks into a rigid cylindrical structure. However, notwithstanding the practical limitations in clamping the core assembly into a rigid structure, it is necessary to restrain lateral movement of the core relative to the reactor vessel to insure that reactivity control elements can be properly inserted into the core at all times.
It is known to mount a loosely assembled reactor core unit in spaced floating relation to a surrounding reactor vessel by means of a plurality of springs arranged between the outer periphery of the core unit and the reactor vessel. While the known spring arrangements for use in restraining lateral movement of a reactor core relative to its associated reactor vessel have proven generally satisfactory when the core undergoes generally radially outward, tangential and limited vertical movement, and are generally capable of restoring the core to a nominal position within the reactor vessel, the prior spring arrangements have not been capable of satisfactory operation in absorbing the seismic energy levels attained during seismic disturbances of the core and yet fit within the space available between the reactor core and associated reactor vessel. To overcome this problem, bilinear spring rate multi-directional spring packs have been developed such as disclosed in U.S. Pat. No. 4,073,685.